X*-HPD R & D (*Scintillator Crystal +small PM) G. Hallewell Centre de Physique des Particules de Marseille KM3NeT meeting, Pylos, Greece, April 16-18, 2007

Some history… By Esso Flyckt X-HPD history

The first xtal-HPD: Philips SMART : P47 phosphor (YSO:Ce) ~30 made (1980s-1992) Philips investment ~ $1M X-HPD history

8 grains of Sb (deposition of PC) Sb deposition shield (+25kV) Domed +25kV surface P47 (YSO:Ce) phosphor Deposited on glass

Will allow SIMION® simulations Internal details of SMART 15” (from Photonis Archives) +25kV 0V Electrodes + feedthroughs for antimony evaporation Antimony screen (limits solid angle of p.c.deposition) * * * Ports for connections to in-tube evaporators for K, Cs

Baikal Quasar 370

Multi-piquages (vide + déposition p.c.)

Développement pour NEMO: (Mauro Tiauti, INFN Gênes) X-HPD avec directionalité, basé sur concept QUASAR 370 (Baikal) Scintillateur en YSO ; guide lumière en plexi ; guide lumière en plexi ; 4 x Hamamatsu R6427 9/8” Verrerie prototype par Soffieria Sestese, par Soffieria Sestese, brides en inox brides en inox

(Cesium of photocathode)

Present status (September 2006) : Photonis have made 2 8’’ prototypes to test ‘internal’ photocathode deposition No crystal: metal disk to measure photocurrent Not optimised electrostatically (disk not at sphere centre)

Photonis XP 1807 Photonis XP 1806 Photonis XP 1805 Photonis XP 1804  ~ 30°  ~ 35°  ~ 31°

Present status: Extensive program (June & Sept 2006) of remeasurements of Q.E. of 4 SMARTS & 1 Quasar Acquired by CPPM in early stages of ANTARES (Under Collaboration GIS IN2P3-Photonis) Tests of 4 (15”) SMARTs +1 preproduction Quasar with polar & equatorial illumination Photocathode at virtual ground linked to Keithley picoammeter scintillator carriage at  700V)

Polar & equatorial Q.E. measurements on 4 15” SMARTS + 1 Quasar (June, Sept 2006) We see: Q.E. of 3 of 4 SMARTS still OK, Equatorial enhancement in Q.E., even with this non-optimal electrostatic configuration

Smart under test +5V Green LED Potentiometer adjustment for 5nA photocurrent at North pole ventouse with fibre output Multi-fibre optical conduit SMART Photocathode uniformity test: Intensity calibration

Photocathode uniformity test: (SMART ) p1: 5nA p2: 5.3nA p3: 4.8nA p5: 3.7nA p4: 5.4nA p6: 7.6nA p7: 7.8nA p8: 9.8nA p9: 5.3nA p10: 3.5nA p12: 2.7nA p11: 2.4nA p13: 2.6nA

Photocathode uniformity test: (SMART ) p1: 5nA p2: 5.1nA p4: 5.3nA p5: 5.2 nA p3: 5.6nA p9: 6.9 nA p6: 6.6nA p7: 6.6nA p8: 6.9nA p13: 3.1 nA p11: 3.1nA p10: 3.2nA p12: 3.0nA

Photocathode uniformity test: (SMART ) p1: 5nA p2: 5.4nA p4: 4.8nA p5: 5.4 nA p3: 5.4nA p9: 6.1 nA p6: 7.0nA p7: 6.2nA p8: 5.6nA p13: 3.4 nA p11: 2.9nA p10: 3.0nA p12: 3.3nA

X-HPD ½ scale prototype (208 mm Ø) LYSO 12 Ø × 18 mm Current status (March 2007) of CERN X-HPD R&D (Christian Joram, Andre Bream, Jacques Seguinot)

SMART and Quasar tubes were the first X-HPDs however the use of a disk shaped scintillator didn’t allow to exploit full potential. need to use fast scintillator, e.g. cube or cylinder. Require high light yield  high gain short decay time Low Z preferable  low back scattering coefficient Emission around = 400 nm LY (  / keV  ns  Z eff  BS emission (nm) YAP:Ce182732~ LYSO:Ce25~4064~ LaBr 3 :Ce633047~ LaBr 3 is quite hygroscopic side and top require conductive and reflective coating  define el. potential, avoid light leaking out. Problem: crystals have high refr. index (~1.8)  large fraction of light is trapped inside crystal due to total internal refection.

Concept of a spherical tube with central spatial anode Radial electric field  negligible transit time spread  ~100% collection efficiency  no magnetic shielding required Large viewing angle (d  ~ 3  ) Possibility of anode segmentation  imaging capability (limited!) Sensitivity gain through ‘Double-cathode effect’ T ~ 0.4 QE

Electrostatics (SIMION 3D) Expected performance Viewing angle  120° X-tal hit probability ~ 100% flight time spread ~0.4 ns (RMS) Can be further improved by optimizing bulb geometry.

First build a HPD with metal-cube anode (1 cm 3 ) ‘Proto 0’ Built in CERN plant. measured at Photonis A. Braem et al., NIM A 570 (2007)

Prepare and characterize components for real X-HPD ‘Proto 1’ PMT Photonis XP3102 (25 mm Ø) electrical feedthrough Al coated

Calibration: 1 p.e. = ·10 9 Vs ENF ~ 1.15 PMT XP3102 has very good signal properties.

Test set-up Lab e - accelerator based on pulsed photoelectrons from a CsI cathode. DAQ on digital scope. LeCroy Waverunner LT344. vacuum pump (turbo) P < mbar Pulsed H 2 flash lamp (VUV) MgF 2 sapphire window mirror -U PC = kV collimator CsI photocathode X-HPD anode

Pulse shape on scope. Contributions from individual photoelectrons clearly visible

Charge amplitude for single photoelectrons… and multi-photoelectrons

Calibration of charge amplitude (for single incident photoelectrons) using single photon response of PMT = primary gain of X-HPD

LYSO, E e = 27.5 keV Fit = Gauss + Exp. Wrote a very simple M.C.: Ingredients:  BS + E’ e spectrum + statistics Input:,  Poisson e-e-  BS  BS EeEe E’ e lost ? PMT e - back-scattering from LYSO Single photoelectron spectra are well described by Gaussian + Exponential. Where does the non-Gaussian part come from ? E e -E’ e E.H. Darlington, J. Phys. D, Vol. 8 (1975) 85 Expect to loose <10% of single photoelectrons by a 3  pedestal cut.  single p.e. detection efficiency of X-HPD ~90%

What happens to back scattered electrons in radial E-field of X-HPD ? Low energy electrons (E < 5 keV) are reabsorbed within << 1 ns. For E > 5 keV re-absorption (within ~1 ns) or loss. Depends on hit position and emission angle. X-tal top X-tal side

Timing studies with first electron method clock startclock stop

Summary and Outlook March 2007 X-HPD is an attractive concept for large area photodetection promises higher performance than classical PMT proof of principle OK components characterized Next steps Make X-HPD with LYSO X- anode Test it at CERN and at Photonis + … Improve light extraction from LYSO crystal. Ideas exist.

CERN photocathode ‘transfer’ plant

CPPM test stand CPPM setting up a test stand for X-HPD evaluation

CPPM test stand (1) SMART

CAEN HV for small PMs

Spellman 25kV supply for X-HPD photocathode

‘Nanolase’ 532nm laser by JDS Uniphase

Near future developments Photonis have identified the technique for p.c. deposition as critical to cost – progress in ‘internal deposition’ CERN-Photonis will test the first 8” ‘mushroom’ and pure spherical geometry X-HPDs spring 2007 Parallel crystal studies (CERN-Photonis, also IPN Orsay) At CPPM, measurements of TT,  TT, HT behaviour, -integrated photocurrent, multi-  res, light guides to PM? (Rebuilding test stand: have acquired new hardware, also Simion ® software + Photonis funding of these PhD  and finally {April 12, 2007} we may have a PhD candidate…) Maintaining close collaboration and exchange between Maintaining close collaboration and exchange between Photonis, CPPM, CERN, Genova Photonis, CPPM, CERN, Genova and Moscow (B. Lubsandorshiev) and Moscow (B. Lubsandorshiev)

Some Longer term developments Progress from 8’’ prototypes to larger, up to original 15’’ of Flyckt/Val Aller SMART (Photocathode deposition  internal or quasi-internal processing: Cost/unit driven lower than hemispherical PM of same Ø ?) In parallel, tests of 8” prototypes (Photonis & CERN) in spheres at ANTARES/NEMO/NESTOR (Need to pass to ‘weaponisation’ phase: compatibility with power & r/o system) Development from Baikal 24V  25kV DC-DC supply Low power Cockroft-Walton multiplier: reliability issues, Can we build from designs of TV tube HV supplies (compatibility of reqt?) (huge statistical MTBF sample + Photonis-Philips connection)

 Pure spherical geometry X-HPDs based on Flyckt/Van Aller Philips SMART tube should be very promising Č  – detectors for underwater telescopes Philips SMART tube should be very promising Č  – detectors for underwater telescopes  ~100% photoelectron collection eff. (over 3  Sr) (c.f. 65% over ~ 4  cathode surface area in ‘hemispherical’ PM)  Much larger photocathode area than same Øhemispherical PM  Much larger photocathode area than same Ø hemispherical PM + suppression of  metal cage  Improved Q.E. (transmissive  reflective) over large % of 3   enhanced overall detection effiency  enhanced overall detection effiency  Improved multi-  sensitivity with small PM readout, possible directionality for segmented PC + multi-anode PM  Cost savings: larger water volume instrumented with a given number of photon detectors Conclusion